# What is the horizon?

Usually, the word "horizon" is understood as the visible part of the earth's surface, that is, the line of contact between the sky and the earth or water. However, this term also has several other meanings.

About what the horizon - let's talk in this article.

## Definitions of the term "horizon"

The second meaning of the word is "visible area around the beholder". For example, a wide horizon opens from the highest point of Mount Everest.

Also, the term "horizon" is used in some highly specialized areas. So, the word has the interpretation "level of something." For example, under the "horizon" understand the height of water in a pond or soil - the horizon of mountain waters. Another definition in a highly specialized focus is the association of rock strata. For example, the ore horizon.

In addition, the concept has a figurative meaning. For example, under the "horizon" also understand a certain range of knowledge, skills or ideas - a specialist with a wide horizon. It is also customary to understand the word "future opportunities and actions." For example, the scientist Pavlov has big horizons.Or another figurative meaning of the word is a sphere of activity. For example, Peter appeared on the horizon of Mary.

Let's take a closer look at the word "horizon" as the visible part of the Earth.

## Horizon as the boundary of visible space

In general, the concept of "horizon" literally translates from Greek into Russian as "limiting."

The boundary that forms when the earth or water surface merges with the sky is also called the horizon line. In open space, the horizon line is a circle.

There are four sides of the horizon - north, south, west, east. If a person is able to determine the side of the horizon, then he is able to navigate the terrain.

Highlight the visible and true horizon.

### Visible horizon

The line bordering the sky and the earth or water is considered the visible horizon. It also includes the separately visible area of the air or earth surface, as well as the visible area around the person who is looking. For example, the boat disappeared over the horizon.

In a different way, the visible horizon is also called the skyline, the skyline and the horizon in terms of space, which can be glimpsed.

### True horizon

In this case, understand the circle of the celestial sphere. In this case, its plane is perpendicular to the plumb line, which passes through the middle of the sphere.

The true horizon divides the celestial sphere into two parts, one of which can be observed from the earth's surface.

The visible and true horizons do not coincide due to the fact that the surface of the Earth is uneven, as well as due to the fracture of light rays.

In another way, the true horizon is also called mathematical or astronomical.

The device with which help determine the true horizon, has the name "artificial horizon". In aviation, an instrument located on board is an artificial horizon.

## Distance to horizon

If a person is in an open area, then the distance to the visible horizon will depend primarily on the observation point and its height above the earth’s surface or water surface.

For example, if an observer is in the steppe at a height of two meters from the surface of the Earth, then the distance to the horizon will be about five meters. If the observer will sit in the boat and the height will be about a meter, then the distance to the horizon will be about three meters.

That is, the higher the point, the farther the horizon. If the observer climbs the twenty-meter tower, then the horizon will stretch tens of kilometers in front of him.

To determine the distance to the horizon, use the formula where the Earth's radius and the height of the observation, then this number is squared and the Earth's radius is taken in the square. And, finally, the resulting number is raised to a power of 1/2.